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  • 1.
    Kallner Bastviken, Sofia
    et al.
    IFM Biology, Linköping University, Campus Valla, Sweden.
    Weisner, Stefan E.B.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Thiere, Geraldine
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Svensson, Jonas M.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Ehde, Per Magnus
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Tonderski, Karin S.
    IFM Biology, Linköping University, Campus Valla, Sweden.
    Effects of vegetation and hydraulic load on seasonal nitrate removal in treatment wetlands2009In: Ecological Engineering: The Journal of Ecotechnology, ISSN 0925-8574, E-ISSN 1872-6992, Vol. 35, no 5, p. 946-952Article in journal (Refereed)
    Abstract [en]

    Optimising nitrate removal and identifying critical factors for nitrate removal in wetlands is an important environmental task in the effort to achieve better surface water quality. In this study, eighteen free water surface wetlands with similar shape and size (22 m2 each) received groundwater with a high nitrate-N concentration (about 11 mg l−1). The effects of two hydraulic loads, 0.13 m d−1 and 0.39 m d−1, and three vegetation types – emergent, submersed and freely developing vegetation – on the nitrate-N removal were investigated through mass inflow and outflow measurements.

    No significant difference in nitrate removal between the different hydraulic loads could be detected. Significantly higher area-specific nitrate removal and first-order area-based rate coefficients were found in the basins with emergent vegetation, with no difference between the basins with submersed and freely developing vegetation. The nitrate-N removal increased as the wetlands matured and the vegetation grew denser, emphasizing the role of dense emergent vegetation for nitrate removal at high nitrate concentrations.

  • 2.
    Persson, Anders
    et al.
    Department of Ecology, Limnology, Ecology Building, Lund, Sweden.
    Svensson, Jonas M.
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS), Environmental Science, Wetland Research Centre.
    Effects of benthivorous fish on biogeochemical processes in lake sediments2006In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 51, no 7, p. 1298-1309Article in journal (Refereed)
    Abstract [en]

    1. Studies of aquatic environments have shown that community organisation may strongly affect ecosystem functioning. One common phenomenon is a change in nutrient level following a shift in the fish community composition. Although several hypotheses have been suggested, there is no consensus on which mechanisms are involved. Our study evaluated indirect effects of benthivorous fish on the biogeochemical processes at the sediment-water interface separately from direct effects caused by nutrient excretion or sediment resuspension.

    2. We assigned field enclosures to three treatments representing typical pond communities; without fish, addition of approximately 10 small tench or addition of one large bream. After one summer, we monitored the water chemistry, benthic invertebrates and periphyton in the enclosures and sampled sediment cores for laboratory analysis of biochemical process rates (oxygen, phosphorus and nitrogen exchange between sediment and water, and denitrification rate).

    3. Fish had strong negative effects on benthic invertebrates, but weaker effects on periphyton, organic content and porosity of the sediment. Moreover, there were significant positive fish effects on both phosphorus and nitrogen concentrations in the water. However, there were no general treatment effects on sediment processes that could explain the treatment effects on water chemistry in the enclosures.

    4. Hence, overall treatment effects attenuated along the chain of interactions. We conclude that the observed effect of benthic fish on water chemistry was probably because of direct effects on nutrient excretion or resuspension of sediment. The similarity between bream and tench treatments suggests large niche complementarity despite their different habitat preferences.

  • 3.
    Persson, Anders
    et al.
    Department of Ecology, Limnology, Lund University, Lund, Sweden.
    Svensson, Jonas M.
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS), Environmental Science, Wetland Research Centre.
    Vertical distribution of benthic community responses to fish predators, and effects on algae and suspended material2006In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 40, no 1, p. 85-95Article in journal (Refereed)
    Abstract [en]

    The vertical positioning of benthic invertebrates should be a trade-off between the risky, but productive, sediment surface and the safer, but physiologically harsher, conditions deeper down in the sediment. This is because the foraging efficiency of benthic fish decreases with sediment depth, whereas the sediment surface is generally better oxygenated and has a higher resource quality than lower layers. We studied how two benthic fish predators, bream (Abramis brama) and ruffe (Gymnocephalus cernuus), affected the community composition and vertical distribution of benthos, and their indirect effects on algae and suspended material, in field enclosures. Whereas bream had significant effects on the density, composition and distribution of the benthos, ruffe had no such effects. The total benthos biomass in bream treatments was an-order of magnitude lower in the upper sediment layer (0-1 cm) and three times lower in the middle layer (1-3 cm) than in the controls, whereas there were no significant effects in the deepest layer (3-10 cm). Bivalves persisted in the deepest layer although their density was reduced in shallow sediment, whereas gastropods faced the risk of local extinction in the presence of bream. As indirect effects, small-bodied cladocerans, phytoplankton, periphyton and both organic and inorganic suspended material were higher in the bream treatments. We conclude that the impact of bream diminished substantially with increasing sediment depth, enabling invertebrates to survive in the sediment and to persist in the presence of bream. However, there were no indications of any group adjusting their vertical position behaviourally as a response to predation threat.

  • 4.
    Weisner, Stefan E.B.
    et al.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Strand, John A.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Sahlén, Göran
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Thiere, Geraldine
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Ehde, Per Magnus
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Svensson, Jonas M.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Combating eutrophication and biodiversity loss in Sweden: importance of constructed wetlands in the agricultural landscape2007In: Multifunctions of wetland systems, Padua: PAN , 2007, p. 60-61Conference paper (Other academic)
    Abstract [en]

    The results of this evaluation show that constructed wetlands in the agricultural landscape are capable of a substantial reduction of the nutrient transport to downstream recipients, but only if properly located. These wetlands will also contribute to an increased biodiversity even if not planned primarily for this purpose. The use of wetlands for multiple functions needs to be developed to motivate large-scale wetland construction.

  • 5.
    Weisner, Stefan
    et al.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Svensson, Jonas M.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Strand, John A.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Svengren, Henrik
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Wetland Research Centre.
    Combating eutrophication in Sweden: Importance of constructed wetlands in agricultural landscapes2005In: Is living water possible in agricultural areas?: Seminar on ecological engineering tools to combat diffuse pollution: June 20-22, 2005, Norway: Proceedings from NJF seminar no. 374 / [ed] Bent C. Braskerud, Ås, Norway: Jordforsk , 2005, p. 66-69Conference paper (Other academic)
    Abstract [en]

    The Wetland Centre at Halmstad University was commissioned by the Swedish Environmental Protection Agency and the Swedish Board of Agriculture to evaluate the effects of artificially created wetlands in Sweden between the years 1996 and 2002 with regard to nutrient retention and biodiversity. The creation of these wetlands has been financed either by Rural Development Support (RDS: Miva, Project support or Lmiva without Project support) or by Local Investment Programmes (LIP). The results are presented separately for the four different categories of constructed wetlands:

    • Constructed wetlands financed by LIP (Local Investment Programmes) (1998-2002).
    • Constructed wetlands financed by PS (Project Support) (2000-2002).
    • Constructed wetlands financed by Miva (Restoration and Establishment of Wetlands and Ponds on Arable land and Semi-natural Grazing land) (1996-1999).
    • Constructed wetlands financed by Lmiva (RDS wetlands that only get management support) (2000-2002).

    The main purpose of this study has been to evaluate the extent to which wetlands created by means of these different support systems have contributed to reduced eutrophication and increased biodiversity. The purpose has not been to evaluate individual wetlands but to give an overview of the differences in efficiency between the various support systems and, to some extent, the difference in results between various geographical regions within Sweden. It has therefore been necessary to include a large number of wetlands in the evaluation, which means that extensive field sampling in the individual wetlands has not been possible. The estimates concerning nutrient retention has therefore been based on modelling, and the biodiversity has been assessed by using dragonflies (Odonata) as indicator organisms.

    Information on 908 wetlands with a total area of 2860 hectares financed by RDS has been compiled and registered. In terms of area, these wetlands divide into 1815 ha financed by Miva, 920 ha financed by PS and 125 ha by Lmiva. In addition, 274 wetlands created by means of LIP, with a total area of 439 ha, have been registered. Field surveys and sampling has been conducted in more than 100 wetlands randomly selected from this register. It is mainly the results from these selected wetlands that are presented here.

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